This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-15802 filed on Jan. 25, 2000.
1. Field of the Invention
The present invention relates to a fuel supply amount controller suitable for use in an internal combustion engine.
2. Description of the Related Art
U.S. Pat. No. 5,044,344 discloses a fuel supply apparatus used for an internal combustion engine. In U.S. Pat. No. 5,044,344, a fuel pump supplies a compressed fuel from a fuel tank to a fuel injector, and the fuel pump works in accordance with electric signals. A check valve is provided between a fuel pump outlet and the fuel injector to prevent the fuel from flowing back from the injector to the pump. A pressure sensor is provided between the pump outlet and the check valve, and connects with an electronic circuit. The electronic circuit feeds an electric energy as a function of pressure inside a fuel supply pipe into the fuel pump. A pressure regulator is provided between the check valve and the engine in the fuel supply pipe. When the pressure inside the fuel supply pipe increases excessively, the excessive fuel returns from the fuel supply pipe into the fuel tank through a return pipe. In this way, the pressure regulator controls the fuel pressure inside the fuel supply pipe to be constant.
However, in U.S. Pat. No. 5,044,344, the fuel pressure is maintained at the pressure set by the pressure regulator while the engine does not work. Thus, when a nozzle of the injector is not sufficiently sealed, the fuel leaks into an intake air pipe, and air-fuel ratio becomes rich at next engine start, thereby exhausting a large amount of deleterious gas, especially hydrocarbon (HC).
Further, a fuel supply apparatus in which a pressure regulator is provided between a fuel pump and a check valve is considered. In this apparatus, a return pipe, which returns excessive fuel from the pressure regulator into the fuel tank, is shortened.
However, in this apparatus, the pressure regulator is provided at the upstream side of the pressure regulator. Thus, even when the fuel temperature and pressure rise at an engine stop, the fuel pressure inside a delivery pipe is continuously high, so that the above-described problem arises.
For solving the problem, U.S. Pat. No. 5,651,347 discloses a fuel supply system in which a fuel pump keeps running within a predetermined period even after an engine stops for decreasing a fuel pressure. However, this system does not include a pressure regulator, and controls the fuel pressure inside the delivery pipe by using a discharge pressure of the fuel pump while the engine works. Thus, the fuel pump needs to be driven even after the engine stops for decreasing the fuel pressure, so that consumed electric power is increased, thereby worsening fuel consumption.
An object of the present invention is to suppress a fuel leak from an injector when an engine stops, without wasting electric power.
According to a first aspect of the present invention, a pump control means controls a fuel pump so that fuel pressure supplied into the internal combustion engine becomes lower than a predetermined fuel pressure regulated by a fuel pressure regulation means when the operating state of the internal combustion engine is within a predetermined operating state.
Thus, the fuel pressure has already been controlled low while the engine state is within the predetermined operating state, so that the fuel leak from the injector during an engine stop is suppressed, thereby reducing an exhaust of deleterious gas when the engine starts again. Further, since the fuel pressure is decreased while the engine works, electric power is not wasted for decreasing the fuel pressure.
According to a second aspect of the present invention, the pump control means ON/OFF controls the fuel pump. The pump control means estimates fuel pressure based on ON period or OFF period of the fuel pump and an opening period of a fuel injection valve, and controls so that the estimated fuel pressure becomes lower than the predetermined fuel pressure.
Thus, there is no need to use a fuel pressure sensor, thereby reducing a manufacturing cost.
According to a third aspect of the present invention, the pump control means duty-controls the fuel pump. The pump control means estimates fuel pressure based on a driving duty of the fuel pump and an opening period of a fuel injection valve, and controls so that the estimated fuel pressure becomes lower than the predetermined fuel pressure.
Thus, there is no need to use a fuel pressure sensor, thereby reducing a manufacturing cost.
According to a fourth aspect of the present invention, the operating state detection means detects the operating state of the internal combustion engine is an idle operating state. The pump control means controls the fuel pump so that pressure of the fuel supplied into the internal combustion engine becomes lower than the predetermined fuel pressure when the operating state detection means detects the operating state of the internal combustion engine is the idle operating state.
Thus, when the engine stops through the idle operating state, the fuel pressure has already decreased, so that the fuel pressure is decreased without driving the fuel pump after the engine stops. Generally, since the operating state is the idle operating state before the engine stops, the fuel pressure is decreased before the engine stops with certainty.
According to a fifth aspect of the present invention, the operating state detection means detects an opening of a throttle valve. The pump control means controls the fuel pump so that pressure of the fuel supplied into the internal combustion engine becomes lower than the predetermined fuel pressure when the operating state detection means detects the throttle valve is full-closed.
Thus, when the throttle valve is full-closed, for example a vehicle speed is reduced, additional fuel pressure is not charged, thereby improving fuel consumption. When the engine stops after the throttle valve is full-closed, for example a vehicle speed is reduced, the fuel pressure has already been decreased, so that the fuel pressure is decreased without driving the fuel pump. Further, when the engine stops after the vehicle speed is reduced, the fuel pressure acting on the injector is decreased before the engine stops with certainty.